Miragaia longicollum

Miragaia (named after Miragaia, the parish in Portugal and geologic unit where its remains were found) is a long-necked stegosaurid dinosaur. Its fossils have been found in Lower Jurassic rocks in Portugal. Miragaia has the longest neck known for any stegosaurian, which included at least seventeen vertebrae.

Miragaia longicollum
Temporal range: Late Jurassic, 150 Ma
Miragaia longicollum (fossil)
Skeleton model
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Order: Ornithischia
Suborder: Stegosauria
Family: Stegosauridae
Subfamily: Dacentrurinae
Genus: Miragaia
Mateus et al., 2009
Species:
M. longicollum
Binomial name
Miragaia longicollum
Mateus et al., 2009

Discovery

Miragaia longicollum vertebra
One of the seventeen neck vertebrae, seen from the right upper side

Miragaia is based on holotype ML 433, a nearly complete anterior half of a skeleton with partial skull (the first cranial material for a European stegosaurid).[1] The remains were found after the construction of a road between the villages of Miragaia and Sobral. The rear half of the skeleton was probably destroyed by the roadcut. The fossils were dug up in August 1999 and August 2001.[2] Among the recovered bones were most of the snout, a right postorbital, both angulars of the lower jaws, fifteen neck vertebrae (the first two, which articulated with the skull, were absent), two anterior dorsal vertebrae, twelve ribs, a chevron, the shoulder bones, most of the forelimbs including a possible os carpi intermedium, a right first metacarpal and three first phalanges; and thirteen bony plates plus a spike.[1] The bones were not articulated but dispersed over a surface of about five to seven metres, though there was a partial concentration of fossils that could be salvaged within a single block.[2] ML 433 was found in the Miragaia Unit of the Sobral Unit, Lourinhã Formation, which dates to the late Kimmeridgian-early Tithonian (Late Jurassic, approximately 150 million years ago).[1]

Octávio Mateus, Susannah Maidment and Nicolai Christiansen named and briefly described Miragaia in 2009. The type species is Miragaia longicollum. The generic name refers to the village of Miragaia but also is an allusion to mira, "wonderful" in Latin, and Gaia, the Earth Goddess. The specific name means "long neck" from the Latin longus, "long" and collum, "neck". A partial pelvis (ilium and pubic bone) and two partial dorsal vertebrae from a juvenile individual (specimen ML 433-A) were found at the same location, intermingled with the bones of the holotype, and were also assigned, as a paratype, to M. longicollum.[1]

Casts were made of the holotype bones and partially based on these a life-size skeletal model was constructed from polyurethane and polyester resin parts.[2]

Alberto Cobos et alii in 2010 noted that all the diagnostic characters of Miragaia longicollum are based on skeletal elements that are absent in the Dacentrurus holotype found in England in layers of about the same age, while all traits that can be compared are shared by both genera. Cobos et alii therefore proposed that Miragaia is a junior synonym of Dacentrurus, meaning that it is the same dinosaur, because it is not possible to differentiate the two taxa through their holotypes.[3]

Description

Size and diagnosis

Miragaia longicollum Scale
Size comparison

The total length of Miragaia has been estimated at 5.5 – 6 metres (18–20 ft).[4] In 2010, Gregory S. Paul estimated the length at 6.5 metres, the weight at two tonnes.[5] Histology shows that the holotype specimen was about 21 years old.[6]

The describers established six distinguishing traits. At their very midline, the praemaxillae meet in a small sharp point, set within a larger notch in the snout tip as a whole. The front lower side edge of the praemaxilla protrudes to below. At least seventeen cervical vertebrae are present. The neural spines of the middle cervical vertebrae have a notch at their lower front edge with immediately above it a process directed to the front. The vertebrae of the middle neck, rear neck and front back possess neural spines that have a transversely expanded upper end. On the neck two rows of triangular bony plates are present that have a lightly convex outer side and a notch at the upper front edge creating a hook.[1]

Neck elongation

Miragaia BW
Restoration

The most notable feature of Miragaia is its long neck, which was composed of at least seventeen vertebrae. According to the authors, this represents the culmination of a trend towards longer necks seen in stegosaurians. The Thyreophora, the larger group they belong to, originally seem to have had nine neck vertebrae and this is also the number shown by the basal stegosaurian Huayangosaurus. Later forms like Stegosaurus or Hesperosaurus had twelve or thirteen. Remarkably Miragaia had more neck vertebrae than most sauropods, a different group of dinosaurs famous for their long necks, which contrasts with the traditional view of stegosaurians as low browsers with short necks. Only the Chinese sauropods Euhelopus, Mamenchisaurus and Omeisaurus had as many neck vertebrae as Miragaia, with most sauropods of the Late Jurassic possessing only twelve to fifteen. Mateus and colleagues suggested that the long neck either allowed Miragaia to browse at a level that other herbivores were not exploiting, or that the neck arose due to sexual selection. The possible food gathering function of the neck makes sexual selection a less plausible explanation, but is not in itself entirely convincing: though the contemporary Iberian sauropods Lusotitan, Dinheirosaurus and Turiasaurus were all very large and might not have competed with a medium-height browser, the niche partitioning is still problematic because in Iberia stegosaurian remains have been referred to Dacentrurus and Stegosaurus, which would have possessed a feeding envelope or feeding height stratification overlapping that of Miragaia.[1]

In sauropods, great neck length was achieved by a combination of three processes: incorporation of back vertebrae into the neck; addition of new vertebrae; and lengthening of the individual neck vertebrae. The authors considered whether these mechanisms might have been paralleled in stegosaurians. The long neck of Miragaia appears to have resulted mostly from back vertebrae becoming incorporated into the neck, based on vertebral counts of other stegosaurians. In this group the total number of prescral vertebrae, of the back and neck combined, hardly increased, but there is a clear transformation, dorsal vertebrae of the back becoming "cervicalised" into cervical vertebrae of the neck. Whereas Huayangosaurus still possessed sixteen back vertebrae, this number was reduced to thirteen in Hesperosaurus. There is currently — no count of the number of dorsal vertebrae being possible — no evidence that with Miragaia new vertebrae contributed to the neck; instead, the distribution of existing vertebrae in the back and neck probably changed, about four extra vertebrae becoming cervicals. There is some evidence for increasing vertebral length in Miragaia and Stegosaurus, compared to more basal species, but this is equivocal and could be due to post-mortem distortion; this mechanism was seen as a minor factor in neck elongation.[1]

The authors also discussed the possible underlying genetic mechanisms for such changes. They pointed out that, in contrast with mammals which almost always have seven neck vertebrae due to as much as four hox-genes ensuring a strict partitioning between neck and back, in extant dinosaurs such as the chicken only a single hox-gene regulates this process, seemingly leading to greater evolutionary plasticity.[1]

Skeleton

Miragaia Right Humerus def
The right humerus, with the arrow indicating the deltopectoral crest

Apart from the neck length, the known osteology of Miragaia resembles that of other stegosaurids, differing in small details. The tip of the beak was toothless, as in Stegosaurus. The upper beak, formed by the praemaxilla, was pendant. The notch in the snout tip was, seen from above, shaped like a W, whereas in Stegosaurus the notch is U-shaped, with a little bulbous projection in the middle. The upper surface of the nasal bone was ornamented. A ridge formed the contact with the maxilla. The maxilla had sixteen teeth. The postorbital was a small and triradiate element.[1]

The cervical vertebrae had well-developed cervical ribs, fused to the vertebral body. The ribs were elongated, with a forward-pointing process on the capitulum, the main rib head. The neural spines of the rear cervicals and front dorsals are transversely expanded at their upper ends due to rugosities serving as an attachment for tendons. This expanded sector projects to the front also, creating a notch on the lower front edge. Additionally the neural spine base is transversely constricted. Ridges extend to the rear from the sides of the neural spine base, over the upper sides of the rear joint processes, the postzygapophyses. These postzygapophyses themselves project far beyond the rear facet of the vertebral body, a derived trait. The prezygapophyses to the contrary, are much shorter; they have a notch at the front upper edge.[1]

The scapula had a large rectangular acromion, with a sharp upper corner, on the lower front edge. The more narrow coracoid had a rounded lower edge. Both the upper arm and ulna and radius (lower arm bones) are also comparable to those of Stegosaurus. The tuberosity of the rear humerus serving as attachment for the musculus triceps brachii is well-developed but the vertical ridge running from it to below is not. In the pelvis, the pubic bone had a deep front part, the processus praepubicus, with a little upward projecting process as seen in Dacentrurus; the rear shaft had a lightly expanded tip.

Osteoderms

Miragaia, like all known stegosaurians, showed an array of plates and spikes, consisting of skin ossifications or osteoderms. Paired triangular plates ran down the midline of the neck, reconstructed as eight pairs. They were asymmetrical with a convex outer side and a concave inner side. Their bases were not very expanded with the exception of a possible last pair, located on the front back. They were obtuse but lightly hooked at the front.[1] A rather long, narrow and straight preserved spike was at first considered to have been a shoulder spine, but was later seen as part of some tail arrangement.

Phylogeny

Miragaia was placed in the Stegosauridae in 2009. Mateus and colleagues performed a phylogenetic analysis and found Miragaia to group with Dacentrurus in a clade Dacentrurinae, newly named for the occasion, the sister group to Stegosaurus (the latter genus was in the cladistic analysis considered to include Hesperosaurus and Wuerhosaurus).[1]

The position of Miragaia in the stegosaurid evolutionary tree is shown by this cladogram:[1]

Stegosauridae

Kentrosaurus

Loricatosaurus

Dacentrurus

Miragaia

Stegosaurus

Wuerhosaurus (=Stegosaurus homheni Maidment et al. 2008)

Hesperosaurus (=Stegosaurus mjosi Maidment et al. 2008)

The authors stressed that the only synapomorphy, shared derived trait, supporting the Dacentrurus-Stegosaurus clade was the possession of the long cervical postzygapophyses, and that these are in fact unknown for Decentrurus itself, so that its close position to Stegosaurus was merely based on the new data provided by the description of Miragaia.[1]

See also

References

  1. ^ a b c d e f g h i j k l m n Mateus, Octávio; Maidment, Susannah C.R.; Christiansen, Nicolai A. (2009-05-22). "A new long-necked 'sauropod-mimic' stegosaur and the evolution of the plated dinosaurs". Proceedings of the Royal Society B: Biological Sciences. The Royal Society. 276 (1663): 1815–1821. doi:10.1098/rspb.2008.1909. PMC 2674496. PMID 19324778.
  2. ^ a b c Araújo, Ricardo; Mateus, Octávio; Walen, Aart; Christiansen, Nicolai (January 2009). "Preparation techniques applied to a stegosaurian dinosaur from Portugal" (PDF). Journal of Paleontological Techniques. 5: 1–23.
  3. ^ Cobos, Alberto; Royo-Torres, Rafael; Luque, Luis; Alcalá, Luis; Mampel, Luis (July 2010). "An Iberian stegosaurs paradise: The Villar del Arzobispo Formation (Tithonian–Berriasian) in Teruel (Spain)". Palaeogeography, Palaeoclimatology, Palaeoecology. 293 (1–2): 223–36. Bibcode:2010PPP...293..223C. doi:10.1016/j.palaeo.2010.05.024.
  4. ^ Mike (25 February 2009). "New Long-Necked Stegosaurs Discovered". Everything Dinosaur Blog. Archived from the original on 13 June 2018.
  5. ^ Paul, Gregory S. (2010). The Princeton Field Guide to Dinosaurs. Princeton University Press. p. 223. ISBN 978-0-691-13720-9.
  6. ^ Waskow, Katja; Mateus, Octávio (April 2017). "Dorsal rib histology of dinosaurs and a crocodylomorph from western Portugal: Skeletochronological implications on age determination and life history traits" (PDF). Comptes Rendus Palévol. 16 (4): 425–39. doi:10.1016/j.crpv.2017.01.003.

External links

Dacentrurus

Dacentrurus (meaning "tail full of points"), originally known as Omosaurus, was a large stegosaur of the Late Jurassic Period (154 - 150 mya) of Europe. Its type species, Omosaurus armatus, was named in 1875, based on a skeleton found in the Kimmeridge Clay of England. In 1902 the genus was renamed Dacentrurus because the name Omosaurus had already been used for a crocodylian. After 1875, half a dozen other species would be named but perhaps only Dacentrurus armatus is valid.

Finds of this animal have been limited and much of its appearance is uncertain. It was a heavily built quadrupedal herbivore, adorned with plates and spikes.

Dinheirosaurus

Dinheirosaurus is a genus of diplodocid sauropod dinosaur that is known from fossils uncovered in modern-day Portugal. It may represent a species of Supersaurus. The only species is Dinheirosaurus lourinhanensis, first described by José Bonaparte and Octávio Mateus in 1999 for vertebrae and some other material from the Lourinhã Formation. Although the precise age of the formation is not known, it can be dated around the early Tithonian of the Late Jurassic.

The known material includes two cervical vertebrae, nine dorsal vertebrae, a few ribs, a fragment of a pubis, and many gastroliths. Of the material, only the vertebrae are diagnostic, with the ribs and pubis being too fragmentary or general to distinguish Dinheirosaurus. This material was first described as in the genus Lourinhasaurus, but differences were noticed and in 1999 Bonaparte and Mateus redescribed the material under the new binomial Dinheirosaurus lourinhanensis. Another specimen, ML 418, thought to be Dinheirosaurus, is now known to be from another Portuguese diplodocid. This means that Dinheirosaurus lived alongside many theropods, sauropods, thyreophorans and ornithopods, as well as at least one other diplodocid.

Dinheirosaurus is a diplodocid, a relative of Apatosaurus, Diplodocus, Barosaurus, Supersaurus, and Tornieria. Among those, the closest relative to Dinheirosaurus is Supersaurus.

List of Ice Age characters

The following is a list of the characters in the Ice Age films, mentioned by a name either presented in the films or in any other official material. Each character includes a summary when possible, the voice actor or actors associated with the character, and a description of the character along with any aliases, spouses and the character's species.

Paranthodon

Paranthodon ( pə-RAN-thə-don) is a genus of stegosaurian dinosaur that lived in what is now South Africa during the Early Cretaceous, between 139 and 131 million years ago. Discovered in 1845, it was one of the first stegosaurians found. Its only remains, a partial skull, isolated teeth, and fragments of vertebrae, were found in the Kirkwood Formation. British paleontologist Richard Owen initially identified the fragments as those of the pareiasaur Anthodon. After remaining untouched for years in the British Museum of Natural History, the partial skull was identified by South African paleontologist Robert Broom as belonging to a different genus; he named the specimen Palaeoscincus africanus. Several years later, Hungarian paleontologist Franz Nopcsa, unaware of Broom's new name, similarly concluded that it represented a new taxon, and named it Paranthodon owenii. Since Nopcsa's species name was assigned after Broom's, and Broom did not assign a new genus, both names are now synonyms of the current binomial, Paranthodon africanus. The genus name combines the Ancient Greek para (near) with the genus name Anthodon, to represent the initial referral of the remains.

In identifying the remains as those of Palaeoscincus, Broom initially classified Paranthodon as an ankylosaurian, a statement backed by the research of Coombs in the 1970s. In 1929, Nopcsa identified the taxon as a stegosaurid, with which most modern studies agree. In 1981, the genus was reviewed with modern taxonomic techniques, and found to be a valid genus of stegosaurid. A 2018 review of Paranthodon could only identify one distinguishing feature, and while that study still referred it to Stegosauria based on similarity and multiple phylogenetic analyses, no diagnostic features of the group could be identified in Paranthodon.

Stegosauria

Stegosauria is a group of herbivorous ornithischian dinosaurs that lived during the Jurassic and early Cretaceous periods. Stegosaurian fossils have been found mostly in the Northern Hemisphere, predominantly in what is now North America, Europe, Africa, South America and Asia. Their geographical origins are unclear; the earliest unequivocal stegosaurian, Huayangosaurus taibaii, lived in China.

Stegosaurians were armored dinosaurs (thyreophorans). Originally, they did not differ much from more primitive members of that group, being small, low-slung, running animals protected by armored scutes. An early evolutionary innovation was the development of tail spikes, or "thagomizers", as defensive weapons. Later species, belonging to a subgroup called the Stegosauridae, became larger, and developed long hindlimbs that no longer allowed them to run. This increased the importance of active defence by the thagomizer, which could ward off even large predators because the tail was in a higher position, pointing horizontally to the rear from the broad pelvis. Stegosaurids had complex arrays of spikes and plates running along their backs, hips and tails. Their necks became longer and their small heads became narrow, able to selectively bite off the best parts of cycads with their beaks. When these plant types declined in diversity, so did the stegosaurians, which became extinct during the first half of the Cretaceous period.

The first stegosaurian finds in the early 19th century were fragmentary. Better fossil material, of the genus Dacentrurus, was discovered in 1874 in England. Soon after, in 1877, the first nearly-complete skeleton was discovered in the United States. Professor Othniel Charles Marsh that year classified such specimens in the new genus Stegosaurus, from which the group acquired its name, and which is still by far the most famous stegosaurian. During the latter half of the twentieth century, many important Chinese finds were made, representing about half of the presently known diversity of stegosaurians.

Stegosauridae

Stegosauridae is a clade of thyreophoran dinosaurs (armoured dinosaurs) within the suborder Stegosauria. The clade is defined as all species of dinosaurs more closely related to Stegosaurus than Huayangosaurus. The name ‘Stegosauridae’ is thus a stem-based name taken from the well-represented genus – Stegosaurus (meaning ‘roofed lizard’). Fossil evidence of stegosaurids, dating from the Middle Jurassic through the Early Cretaceous, have been recovered from North America, Eurasia and Africa. On the other hand, Stegosauridae's sister clade, huayangosaurids, can be traced only to the Middle Jurassic.The clade Stegosauridae is composed of the genera Stegosaurus, Dacentrurus, Miragaia, Loricatosaurus, and Kentrosaurus, with the last considered to be at the base of the clade. The stegosaurids like all other stegosaurians were quadrupedal herbivores that exhibited the characteristic stegosaurian dorsal dermal plates. These large, thin, erect plates are thought to be aligned parasagittally from the neck to near the end of the tail, where they give way to paired of spikes. Although defense, thermo-regulation and display have been theorized to be the possible functions of these dorsal plates, a study of the ontogenetic histology of the plates and spikes suggests that the plates serve different functions at different stages of the stegosaurids’ life histories. The terminal spikes in the tail are thought to have been used in old adults, at least, as a weapon for defence. However, the function of stegosaurid plates and spikes, at different life stages, still remains a matter of great debate.

Stegosaurids are distinguished from huayangosaurids in that the former have lost the plesiomorphic pre-maxillary teeth and lateral scute rows along the trunk. Furthermore, stegosaurids as opposed to huayangosaurids have long narrow skulls and longer hindlimbs compared to their forelimbs. However, these two features are not diagnostic of Stegosauridae because they may also be present in non-stegosaurids other than huayangosaurids.

Timeline of stegosaur research

This timeline of stegosaur research is a chronological listing of events in the history of paleontology focused on the stegosaurs, the iconic plate-backed, spike-tailed herbivorous eurypod dinosaurs that predominated during the Jurassic period. The first scientifically documented stegosaur remains were recovered from Early Cretaceous strata in England during the mid-19th century. However, they would not be recognized as a distinct group of dinosaurs until Othniel Charles Marsh described the new genus and species Stegosaurus armatus in 1877, which he regarded as the founding member of the Stegosauria. This new taxon originally included all armored dinosaurs. It was not until 1927 that Alfred Sherwood Romer implemented the modern use of the name Stegosauria as specifically pertaining to the plate-backed and spike-tailed dinosaurs.From the time of their earliest description, the chief mystery surrounding stegosaurs was the function of their distinctive back plates. Marsh originally interpreted them as being plates of armor that would protect against predators. In 1910, Richard Swann Lull would agree with this hypothesis. Charles Whitney Gilmore disagreed in 1914 and argued that the only protection a stegosaur could gain from its plates was to appear intimidatingly larger to potential predators. Nearly forty years later, Davitashvili argued that the plates were too fragile to be used for defense and instead used to attract mates and signal the stegosaur's rank in a social hierarchy.In the late 1970s, James O. Farlow and others would propose that the thin, blood vessel-rich plates helped absorb or lose body heat, depending on the animal's own physiological requirements. This hypothesis was put forth in a broader context of scientists considering the possibility that dinosaurs may have maintained body temperatures and activity levels similar to those of modern birds and mammals, in which case the plates may have served primarily to shed heat rather than gain it. In the late 1980s Buffrenil and others revived the idea that stegosaur plates were display structures, an interpretation that would continue to find favor from researchers like Main and colleagues into the 21st century.

Wuerhosaurus

Wuerhosaurus is a genus of stegosaurid dinosaur from the Early Cretaceous Period of China and Mongolia. As such, it was one of the last genera of stegosaurians known to have existed, since most others lived in the late Jurassic.

Languages

This page is based on a Wikipedia article written by authors (here).
Text is available under the CC BY-SA 3.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.